The proposed research concerns a population of end-stage memory CD8 T cells that accumulates during HIV disease progression. CD8 T cells with similar characteristics are generated as the final stage of cell cultures subjected to repeated rounds of antigen-driven proliferation. Cultures that have reached this terminal state of "replicative senescence" are characterized by irreversible cell cycle arrest, apoptosis resistance, shortened telomeres, altered cytokine profiles, reduced anti-viral functions, and permanent loss of CD28 gene expression. Clinical studies have shown that high proportions of CD8 T cells that lack CD28 expression are correlated with reduced antibody response to influenza vaccination and with increased mortality risk in the elderly, as well as with a variety of suppressor cell functions, suggesting that the high proportions of CD8+CD28 - in persons infected with HIV may affect disease progression. The ability to explore these interactions in cell culture model systems provides an unparalleled opportunity to experimentally dissect the genetic and molecular basis of several fundamental aspects of HIV pathogenesis and to evaluate potential immunomodulatory strategies. The following Specific Aims will be addressed: (1) To evaluate the effects of senescence on CD8 T cell function and correlate these findings to HIV-1 infection. Long-term cultures and clones will be used to follow function, cytokine production, and associated phenotypic characteristics during the entire trajectory to senescence. CD8 T cells with similar phenotypes isolated from HIV-infected persons will be tested ex vivo for the corresponding functions and cytokine changes; (2) To explore the indirect effects of CD8 T cell senescence on other immune functions. Cells and cell-free supernatants from senescent versus early passage CD8 T cell cultures will be compared for effects on autologous CD4 T cell function, CD8 effector activity, B cell antibody production and antigen-presentation by dendritic cells. Interactions identified for CD8 T cells that have been "aged" in vitro will be validated using cells with the same phenotype isolated from HIV-infected persons; (3). To determine if strategies that prevent replicative senescence in CD8 T cells also prevent some of the deleterious immune effects identified in Aims 1 and 2. Gene transduction (hTERT, CD28) as well as estrogen effects on the process of replicative senescence will be used to determine the optimal means for maintaining the functional profile of HIV-specific CD8 T cells with respect to both direct and indirect immune effects. This novel approach to analysis of the immune exhaustion in HIV disease may yield promising strategies for immunotherapy to retard or prevent progression to AIDS.